MICROMORPHOLOGICAL ANALYSIS OF SOILS

Examination of soils using the microscope was introduced by W.L. Kubiena in the 1930s. Techniques developed for optical mineralogy have been adapted to study the fabric of soil in thin–section analysis under plain and polarised light. Soil samples with known orientation are taken from the field, dried and set in polyester resin and subsequently cut into thin slices 0.30 μm thick, mounted on microscope slides and examined under the polarising microscope. The soil fabric can be seen to comprise skeleton (mineral) grains, plasma and voids. The disposition of mineral grains, voids and clay domains and the location and appearance of various segregations and concentrations of clay, iron (Fe), manganese and organic matter enable the pedologist to assess the results of soil-forming processes at the microscopic level. The three-dimensional arrangement of these components provides an insight into the detailed processes that operate in soils and can supply evidence of environmental change. scanning electron microscopy (SEM) has carried the examination of soil fabrics into even greater detail. Micromorphology is used, for example, to confirm the presence of clay-skins (cutans) in, for example, luvisols and the presence of organic-iron coatings to mineral grains in podzols. Quantitative micromorphology is sometimes termed micromorphometry.